1. Field of the Invention
The present invention relates to a camera using a recording medium which electronically develops an image obtained by exposing a recording medium, and more particularly, to a device controlling a photographing operation of the camera.
2. Description of the Related Art
Conventionally, there is known a photographic material which electronically develops an optical image formed thereon through a photographing lens. Japanese Unexamined Patent Publication No. 5-2280, for example, discloses a recording material which is a combination of an electrostatic information recording material and an electric charge keeping medium. In this specification, such a recording medium is referred to as an electro-developing recording material, and a camera using the electro-developing recording material is referred to as an electro-developing type camera.
In the electro-developing recording medium disclosed in the above publication, the electrostatic information recording material has a photo conducting layer and an inorganic oxide material layer, and the electric charge keeping medium has a liquid crystal display. In this structure, when the electrostatic information recording material is exposed while an electric voltage is applied to the electrostatic information recording material and the electric charge keeping medium, an electric charge in accordance with the amount of incident light is generated in the electrostatic information recording material. Since the intensity of an electric field applied to the liquid crystal display facing the electrostatic information recording material varies in accordance with the generated electric charge, an image corresponding to the amount of light distribution is indicated or developed on the liquid crystal display.
Japanese Unexamined Patent Publication No. 5-150251 discloses a dispersion type liquid crystal display in which an image indicated on the liquid crystal display is kept even if the electric field applied to the liquid crystal display is removed.
A contrast of the image indicated on the liquid crystal display becomes larger since an electric voltage is started to be applied to the electro-developing recording medium, and when the image is bright, the contrast becomes a maximum when the electric voltage has been applied to the electro-developing recording medium for a predetermined period. Therefore, by stopping the voltage application at that time, an image having a high contrast can be obtained. Conversely, although when the image is dark, the contrast becomes the maximum when the electric voltage has been applied to the electro-developing recording medium for a period longer than the predetermined period, the contrast does not become so high if the voltage applying time is long to some extent. Therefore, the voltage applying time onto the electro-developing recording medium is set so that a contrast having a predetermined degree is obtained.
Nevertheless, when the exposure period for which the electro-developing recording medium is exposed is longer than the voltage applying time, as a result of an exposure calculation based on a photometry value, a problem occurs in which a clear image cannot be recorded on the electro-developing recording medium since the voltage applying is stopped during the exposure. On the other hand, as disclosed in Japanese Unexamined Patent Publication No. 3-278342, by setting an electric voltage, which is applied to the electro-developing recording medium, to a low value, the voltage applying time can be prolonged, but a problem occurs in which the liquid crystal display cannot indicate a clear image if the applied voltage is too low.
On the other hand, if an electronic flash is used for an electro-developing type camera, the radiation of the electronic flash may be performed after the shutter is fully open. However, in a construction in which the electric voltage is applied to the electro-developing recording medium in synchronization with a start of the opening operation of the shutter, a predetermined time needs to pass from the voltage application to the flash radiation. Therefore, the voltage application during the predetermined time cannot be used for the development. Conversely, if the voltage application to the electro-developing recording medium is started prior to the exposure, the contrast of the image formed on the liquid crystal display becomes low since the required voltage difference between a bright portion and a dark portion in the image is difficult to obtain, as described later.